1. Field of the Invention
In an integrated circuit, the invention relates to a bistable circuit that is protected against logic random events and is fast. The bistable circuit may be used especially to make a latch toggle circuit (or latch trigger circuit), a flip-flop toggle circuit (or flip-flop trigger circuit), an SRAM cell, etc. A prior art bistable circuit comprises two inverters coupled upside down to each other and is used to memorize a piece of logic data.
2. Description of the Prior Art
The constant and gradual miniaturization of electronic circuits is making it possible to obtain circuits that perform increasingly well and are ever smaller. As a tradeoff, these circuits are more sensitive to their environment which may give rise to logic random events.
A logic random event is a change in logic state at a specific time or an undesired transitional logic state, at a point of the integrated circuit. Logic random events may have a wide variety of causes and consequences. In a bistable circuit for example, a random event gives rise to a change in content (logic data) of the bistable circuit which would have to be reprogrammed in order to recover its initial value.
To protect bistable circuits, there is a prior art method, described especially in the patent FR 2 833 783, for coupling a capacitive bridge between an input point E and an output point S of the bistable circuit (FIG. 1).
The capacitive circuit increases the critical load of the circuit. It accordingly increases the energy needed by the circuit in order to make it switch over and increases the switch-over time of the bistable circuit. Since random events generally have limited energy, this energy is no longer sufficient to make the bistable circuit flip over, and the bistable circuit is thus protected against random events. However, to program the bistable circuit, i.e. to deliberately prompt the change in logic state of the bistable circuit, it is necessary to provide far greater energy, necessary to load the capacitive bridge, and it is necessary to have much more time than when there is no capacitive bridge. This is also the case obviously for any circuit using a bistable circuit especially for a latch toggle circuit or a flip-flop toggle circuit.